Method for rotationally aligning and degassing semiconductor substrate within single vacuum chamber

ABSTRACT

A semiconductor processing apparatus and process is disclosed which is capable of degassing a semiconductor substrate and also orienting the substrate in the same vacuum chamber. The apparatus includes an electrostatic clamping structure for retaining the entire undersurface of a semiconductor substrate in thermal communication therewith in the vacuum chamber, a heater located within the electrostatic clamping structure for heating the electrostatically clamped substrate to degas it, a rotation mechanism for imparting rotation to the substrate in the vacuum chamber, and a detector for detecting the rotational alignment of the substrate in response to the rotation of the substrate. In a preferred embodiment, the substrate is rotated to rotationally align it as it is being heated to degas it.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.08/383,112 filed Feb. 3, 1995 now U.S. Pat. No. 5,982,986 on Nov. 9,1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to semiconductor substrate processing. Moreparticularly, this invention relates to apparatus and method forrotationally aligning and degassing a semiconductor substrate in thesame vacuum chamber.

2. Description of the Related Art

In the processing of semiconductor substrates or wafers in the formationof integrated circuit structures thereon, it is important that the waferbe thoroughly degassed to remove adsorbed gases, moisture, etc. from thewafer prior to, for example, performing a physical vapor deposition(PVD) process to deposit materials on the wafer by sputtering from atarget in a vacuum processing chamber. Other processes such as advancedchemical vapor deposition (CVD) processing, may also require degassingof the wafer. Degassing prior to PVD processing conventionally iscarried out at temperatures exceeding 350° C. for time periods of fromabout 40 seconds to about 2 minutes to remove sufficient gases from thewafer to assure a satisfactory deposition by sputtering. Outgassing ofsubstrates during aluminum PVD is more severe than during the prior CVDsteps because the PVD process is performed at much higher vacuums andsomewhat higher substrate temperatures, both of which induce greateroutgassing. Therefore, to avoid outgassing from contaminating the PVDprocess, the de-gassing of the wafer before the first PVD step must bemore extensive than the de-gassing performed before the CVD steps.

Degassing of a wafer is conventionally carried out in one of two ways.One method used to degas a wafer comprises a radiant heating of thewafer, using heat lamps located external to the vacuum chambercontaining the wafer, and positioned adjacent transparent windowsthrough which the heat is radiated from the lamps to the wafer. Thismethod is relatively low in cost, is fairly rapid, and does not requireclamping the wafer to the wafer support within the vacuum chamber.However, the radiant heating method is unsatisfactory for temperaturesin excess of 350° C., because the temperature of the wafer is not easilycontrolled, and the heating is usually not uniform across the entirewafer. Typical temperature nonuniformity across the wafer at 350° C. isgreater than ±30° C. Furthermore, alignment of the rotationalorientation of the wafer, during the degassing step, is usually notpossible because the radiation from the heat lamps interferes withoperation of the optical means conventionally used for such rotationalalignment.

The other method conventionally used to degas a wafer, particularly whensubsequent PVD processing will be carried out which requires degassingat temperatures in excess of about 350° C., comprises physically(mechanically) clamping the wafer to a wafer support in a vacuum chamberand then heating the wafer using a resistive heater located in the wafersupport adjacent the undersurface of the wafer resting on the wafersupport. However, since the wafer normally only physically touches thewafer support at the physically clamped periphery or edges of the wafer,and the transmission of heat from the heater in the wafer support to theunderside of the wafer via conduction through a vacuum is very poor, athermally-conductive gas is normally admitted into the space between thewafer support and the underside of the wafer, with the clamped edge ofthe wafer serving to at least partially retain the gas in this space.This heating method permits degassification temperatures of as high asabout 500-600° C. to be achieved.

This method thus permits the use of degassing temperatures in excess of350° C., and permits measurement and reasonable control of thetemperature of the wafer. However, alignment of the rotationalorientation usually cannot be carried out during the degassing stepbecause the conduit for the thermally conductive gas inhibits rotationof the chuck. The clamping ring also inhibits rotation due to itsweight. Rotation of a clamped wafer could also cause wafer breakage andparticles. The alignment of the rotational orientation of the wafermust, therefore, be carried out in a separate chamber prior to thedegassing step. Furthermore, because this form of degassing must bepreformed in a chamber very similar to a PVD chamber (i.e., it mustinclude a cryopump, heated chuck, wafer lift assembly, cryo isolationvalve, transfer chamber, isolation valve, clamp ring, etc.), it is avery expensive solution. Also typical temperature uniformities acrossthe wafer achieved with this type of degassing apparatus areapproximately ±10 to 15° C. Temperature uniformities of ±5° C. arerequired for advanced devices.

Furthermore, regardless of which heating method is used, because of theextended time period needed for degassing prior to PVD processing, thedegassing step can reduce process throughput. One prior art approachwhich has been considered for solving this particular problem is toprovide parallel degassing chambers, i.e., two degassing chambers areprovided in a semiconductor wafer processing apparatus for each PVDprocessing chamber. However, this adds considerable extra cost to theapparatus. In addition, when the rotational orientation of the wafermust also be carried out in a separate chamber, either three or fourpreprocessing chambers must be utilized (depending whether or not eachof the two parallel degassing chamber is coupled to its own separaterotational orientation chamber), which greatly adds to the overallexpense of the apparatus.

It would, therefore, be desirable to be able to consolidate therotational alignment and degassing of the wafer into a single chamberwhich would avoid the expense of separate chambers, as well as theadditional time consumed during transfer of the wafer from one chamberto the other. It would be of further advantage if the degassing could becarried out at high temperatures, i.e., temperatures in excess of about350° C., without mechanically clamping the wafer to the wafer support,and while still maintaining an even and controllable heating of thewafer. It would be even more advantageous if both the degassing and therotational orientation of the wafer could be carried out simultaneouslyin the same chamber at a high temperature and without mechanicalclamping the wafer to the wafer support.

SUMMARY OF THE INVENTION

In accordance with the invention, a semiconductor processing system isprovided which is capable of degassing a semiconductor substrate attemperatures as high as 500° C. and also rotationally aligning thesubstrate in the same vacuum chamber, without the use of a mechanicalclamping ring and thermally conductive gas. The apparatus of thesemiconductor processing system includes a heated electrostatic clampingstructure for supporting the semiconductor wafer and retaining thesubstrate in thermal communication therewith in the vacuum chamber, aheater within the electrostatic clamping structure for heating theelectrostatically clamped substrate to degas it, a rotation mechanismfor imparting rotation to the substrate in the same vacuum chamber, anda detector for detecting the rotational alignment of the substrate inthe vacuum chamber in response to the rotation of the substrate. In apreferred embodiment, the substrate is rotated to rotationally align itas it is being heated to degas it without, however, using mechanicalclamping apparatus to secure the substrate to a substrate support. In analternate embodiment, the substrate may be rotated for alignment eitherprior to or after degassification, but in the same chamber,

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view in schematic form of adegasification and rotational alignment chamber of a semiconductorsubstrate processing apparatus comprising one embodiment of theinvention wherein the substrate is rotationally aligned using a liftring within the vacuum chamber to rotate the substrate.

FIG. 2 is an isometric view illustrating the optical orientationapparatus shown in FIG. 1 for rotationally aligning the substrate.

FIG. 3 is a vertical cross-sectional view in schematic form of adegasification and rotational alignment chamber of a semiconductorsubstrate processing apparatus comprising another embodiment of theinvention wherein the substrate is rotationally aligned by rotation ofthe substrate support and electrostatic chuck therein.

DETAILED DESCRIPTION OF THE INVENTION

The invention comprises a semiconductor processing system capable ofdegassing a semiconductor substrate or wafer at temperatures as high as500° C. or higher, depending upon the temperature sensitivity of othermaterials already on the wafer, and also capable of aligning therotational orientation of the wafer in the same vacuum chamber, withoutthe use of a mechanical clamping ring and thermally conductive gas. Thesystem utilizes an electrostatic clamping means for retaining thesemiconductor wafer in thermal communication with a wafer support in thevacuum chamber while the wafer is heated by a heater within the wafersupport to degas it. A rotation mechanism for imparting rotation to thewafer in the vacuum chamber and a detector for detecting the rotationalalignment of the wafer in response to the rotation of the wafer are alsoprovided. In a preferred embodiment, the wafer is simultaneously rotatedto rotationally align it while it is being heated to degas it.

Turning now to FIG. 1, one embodiment of the system of the invention isgenerally illustrated wherein a vacuum chamber 2 is provided with awafer support 10, which may comprise a stainless steel material, mountedon a pedestal 12. Forming the top surface of wafer support 10 is anelectrostatic clamping means or chuck 20 which, in the illustratedembodiment, comprises an insulative material 24, such as aluminum oxide,aluminum nitride, or other ceramic material, on the top surface of wafersupport 10 and having embedded therein metallic electrodes 26 and 27which are connected through leads 28 and 29 to a high voltage source(not shown) external to vacuum chamber 2. Also embedded within chuck 20is a heater 14, such as a resistance heater, which may be connectedthrough lead(s) 16 to a power source (not shown) external to vacuumchamber 2. The inside of wafer support 10 and pedestal 12 are atatmospheric pressure. Wafer support 10 is brazed to ceramic chuck 20 toprovide a vacuum seal.

A wafer 30, to be degassed and rotationally aligned, may be placed onelectrostatic chuck 20 and electrodes 26 and 27 energized with a highvoltage, e.g., about 500-5000 volts DC, to thereby electrostaticallyclamp wafer 30 to the surface of electrostatic chuck 20. Wafer 30 isremoved from the system transfer robot (not shown) for placement onelectrostatic chuck 20 (and later removal) by lift pins or fingers (notshown) on a ring (also not shown) attached to support plate 51 which, inturn, is connected to a pneumatic or motor-driven lift motor 48 andshaft 50 through a vacuum isolation bellows 54.

Heater 14 is energized to thereby heat electrostatic chuck 20 which thenheats wafer 30 through direct conduction. It should be noted that unlikeprior art securement of the wafer to an upper surface of a wafer supportduring the heating of the wafer, not only is the periphery of the waferin thermal contact with electrostatic chuck 20 (to provide thermalcoupling therebetween), but all of the undersurface of wafer 30 is alsoin mechanical contact with electrostatic chuck 20 and thereforethermally coupled to electrostatic chuck 20 due to the uniformity of theelectrostatic forces across the surface of electrostatic chuck 20.Heater 10 advantageously is activated prior to the electrostaticclamping of wafer 30 to electrostatic chuck 20 to preheat electrostaticchuck 20 and thereby accelerate the heating process. Because of theintimate contact of the wafer to the heated electrostatic chuck, gasbetween the wafer and the chuck is not required.

Wafer 30 is also rotationally aligned in vacuum chamber 2. Alignment ofthe rotational or angular orientation of a semiconductor wafer isnecessary to provide the correct rotational alignment of a semiconductorwafer in a processing chamber, as is well known to those skilled in theart. Such rotational alignment is facilitated by the provision of somesort of alignment indicia on the wafer itself. A common alignment meansis the provision of a flat or notch on one portion of the circumferenceof a normally circular wafer. A beam of light from a light source isthen usually directed perpendicular to the plane of the wafer tointercept the wafer adjacent its edge. As the wafer is rotated, thelight is reflected back to the source until the flat or notched portionis encountered, as which point the light beam is transmitted to a photodetector positioned on the other side of the wafer.

As shown in FIG. 1, a ring 40 may be provided to rotate wafer 30 torotationally align wafer 30 in vacuum chamber 2. When it is desired torotate wafer 30, the wafer is lowered onto rotatable ring 40. Wafer 30is lowered onto ring 40 by activation of fluid powered motor 90 to whichis attached a shaft 92, as shown in FIG. 1, which is centrally mountedwithin pedestal 12. Shaft 92 is coupled to the upper portion of pedestal12 by a cross bar 94. Bellows 13 on pedestal 12 permit the upper portionof pedestal 12, with support 10 and electrostatic chuck 20 securedthereto, to move up and down (vertically) while maintaining the vacuumwithin chamber 2. This, in turn, permits the desired lowering of wafer30 onto rotatable ring 40, and subsequent raising of wafer 30 off ring40 when the orientation step is complete.

Ring 40 is provided with arms 42 which are, in turn, connected to acentral cylinder 44 to which are attached a first set of magnets 46which form a part of magnetic coupling mechanism 52. A hollow shaft 60located within pedestal 12 has a second set of magnets 62 mountedthereon forming the other portion of magnetic coupling mechanism 52. Amotor 64 rotates shaft 60 via a belt 66 and this rotation is transmittedthrough magnetic coupling mechanism 52 to cylinder 44 and ring 40 tothereby rotate wafer 30.

As wafer 30 is rotated on ring 40 by motor 64, a light source 70,external to vacuum chamber 2, directs a light beam 72 through a firstwindow 4 in the top wall of vacuum chamber 2 toward the top surface ofwafer 30 adjacent the periphery thereof. When flat portion or notch 32of wafer 30 is encountered, as shown in FIG. 2, light beam 72 passesthrough to a second window 6 located in the bottom wall of vacuumchamber 2 and is detected by photodetector 80, signifying the rotationalposition of the flat or notched portion 32 of wafer 30.

In the embodiment shown in FIGS. 1 and 2, the rotational alignment ofwafer 30 is carried out in the same vacuum chamber as thedegassification of wafer 30. However, the rotational alignment anddegassification are carried out sequentially, rather thansimultaneously. The rotational alignment may be carried out eitherbefore or after the degassifying of wafer 30.

It would, however, be even more advantageous if, in addition to usingthe same vacuum chamber for both rotational orientation and degassifyingof the wafer, both steps could be carried out simultaneously. FIG. 3illustrates another embodiment of the invention which permits suchsimultaneous rotational orientation and degassifying of a semiconductorwafer by rotating the wafer support and electrostatic chuck with thewafer clamped thereto so that the wafer continues to be heated andtherefore degassified while the rotational orientation of the wafer iscarried out by the light source and photodetector.

In FIG. 3, wherein like elements are identified with like numerals, thepedestal beneath wafer support 10 comprises a hollow cylinder 112 withits cylindrical wall magnetically coupled through magnetic couplingmechanism or clutch 152 to a hollow cylindrical shaft 160 external tovacuum chamber 2. Cylindrical shaft 160 is, in turn, connected to amotor 164 which rotates cylindrical shaft 160 and this rotation istransmitted through magnetic coupling 152 to cylindrical pedestal 112 tothereby rotate wafer support 10, electrostatic chuck 20, and wafer 30clamped thereto.

A flexible heater lead 116 connects heater lead 16 within vacuum chamber2 to an external heater lead 118; while flexible high voltage leads 128and 129 connect high voltage leads 28 and 29 with external high voltagelead 138 and 139. This provision of such flexible leads permits rotationof wafer support 10, for example, 180° in each direction while stillmaintaining electrical contact respectively to heater 14 andelectrostatic chuck electrodes 26 and 27.

As described in the previous embodiment, as wafer 30 is rotated by motor164, light source 70, external to vacuum chamber 2, directs light beam72 through first window 4 in the top wall of vacuum chamber 2 toward thetop surface of wafer 30 adjacent the periphery thereof. When flatportion 32 of wafer 30 is encountered, as previously shown and describedin FIG. 2, light beam 72 passes to and through second window 6 locatedin the bottom wall of vacuum chamber 2 and is detected by photodetector80, signifying the rotational position of flat or notched portion 32 ofwafer 30.

Thus the semiconductor wafer processing system of the invention permitsdegassifying and rotational alignment of a semiconductor wafer to becarried out in the same vacuum chamber with temperatures above 350° C.being utilizable without, however, mechanical clamping the wafer to thewafer support. In a preferred embodiment, rotational alignment anddegassification of the semiconductor wafer may be carried outsimultaneously in the same chamber.

Having thus described the invention what is claimed is:
 1. A process fordegassing a semiconductor substrate and also orienting the substrate inthe same vacuum chamber which comprises: a) providing a vacuum chamber;b) supporting a semiconductor substrate on a heated electrostaticclamping structure functioning as a substrate support for retaining saidsemiconductor substrate in thermal communication therewith in saidvacuum chamber; c) heating said electrostatically clamped substrate insaid vacuum chamber to a temperature sufficiently to degas saidelectrostatically clamped substrate by providing a heater within saidelectrostatic clamping structure; d) rotating said substrate in saidvacuum chamber while heating and degassing said semiconductor substrate;and e) while simultaneously rotating said substrate, and heating saidsemiconductor substrate to degas it, aligning said semiconductorsubstrate in said vacuum chamber using a water alignment mechanismcapable of a detecting the rotational alignment of said substrate inresponse to said rotating of said substrate, said aligning step furthercomprising: i) directing a beam of light perpendicular to the plane ofsaid substrate from a light source on one side of said substrate; andii) detecting said beam of light from said light source with aphotodetector on an opposite side of said substrate when said beam oflight encounters a non-circular portion of said substrate as saidsubstrate rotates.
 2. The process for degassing said semiconductorsubstrate of claim 1 wherein said step of rotating said substratefurther comprises lifting said substrate off said substrate supportusing a rotatable ring within said vacuum chamber.
 3. The semiconductorprocessing apparatus of claim 2 wherein said step of rotating saidsubstrate further comprise magnetically coupling said rotating ring to asource of rotation outside of said vacuum chamber.
 4. A process capableof degassing a semiconductor substrate in a vacuum chamber of asemiconductor processing apparatus and also rotationally aligning saidsubstrate in said vacuum chamber which comprises: a) providing a vacuumchamber; b) supporting a semiconductor substrate on a heatedelectrostatic clamping structure functioning as a substrate support forretaining said semiconductor substrate in thermal communicationtherewith in said vacuum chamber; c) heating said electrostaticallyclamped substrate in said vacuum chamber to a temperature sufficient todegas said substrate via a heater within said electrostatic clampingstructure; d) rotating said substrate in said vacuum chamber up to 180°in either one or both directions using a rotation mechanism; and e)aligning said substrate in said vacuum chamber using a wafer alignmentmechanism capable of determining the rotational alignment of saidsubstrate in response to said rotation of said substrate in said vacuumchamber, said aligning further comprising: i) directing a beam of lightperpendicular to the plane of said substrate from a light source on oneside of said substrate; and ii) detecting said beam of light from saidlight source with a photodetector on an opposite side of said substratewhen said beam of light encounters a non-circular portion of saidsubstrate as said substrate rotates.
 5. The process of claim 4 whereinsaid step of heating said substrate further comprises heating saidsubstrate with a heater comprising a resistance heater in saidelectrostatic clamping structure adjacent a surface of said substratesupport in thermal communication with said substrate.
 6. The process ofclaim 4 wherein said step of supporting a semiconductor substrate on aheated electrostatic clamping structure further comprises clamping saidsubstrate to insulation on the surface of said electrostatic clampingstructure facing an undersurface of said substrate, said insulationhaving one or more high voltage electrodes therein.
 7. The process ofclaim 4 wherein said step of rotating said substrate in said vacuumchamber using a rotation mechanism further comprises rotating saidsubstrate using a rotatable ring within said vacuum chamber.
 8. Theprocess of claim 7 wherein said step of rotating said substrate in saidvacuum chamber using a rotation mechanism further comprises couplingsaid rotatable ring through a magnetic coupling to a source of rotationoutside of said vacuum chamber.
 9. The process of claim 7 wherein saidstep of rotating said substrate in said chamber using a rotationmechanism further comprises using a rotatable heated electrostaticclamping mechanism to permit said substrate to be rotationally alignedwhile said substrate is heated to degas said substrate.
 10. A processcapable of degassing a semiconductor substrate in a vacuum chamber andalso rotationally aligning said substrate in said vacuum chamber whichcomprises: a) providing a vacuum chamber; b) supporting a semiconductorsubstrate on an electrostatic clamping mechanism on a substrate supportwithin said vacuum chamber to retain said semiconductor substrate inthermal communication with said substrate support in said vacuumchamber, said electrostatic clamping mechanism comprising insulation onthe surface of said substrate support facing an undersurface of saidsubstrate, and a high voltage electrode in said insulation; c) heatingsaid substrate with a heater within said electrostatic clampingmechanism capable of heating said electrostatically clamped substrate insaid vacuum chamber to a temperature in excess of 350° C. to degas saidsubstrate; d) rotating said substrate in said vacuum chamber using arotation mechanism capable of imparting rotation to said substrate insaid vacuum chamber comprising: i) a rotatable ring within said vacuumchamber; and ii) a magnetic coupling to couple said rotatable ring to asource of rotation outside of said vacuum chamber; and e) aligning saidsubstrate in said vacuum chamber using a wafer alignment mechanismcapable of determining the rotational alignment of said substrate inresponse to said rotation of said substrate in said vacuum chamber, saidaligning further comprising: i) directing a beam of light perpendicularto the plane of said substrate from a light source on one side of saidsubstrate located outside of said vacuum chamber, said light sourcecapable of directing said beam of light through a first window in afirst wall of said vacuum chamber; and ii) detecting said beam of lightwith a photodetector located outside of said vacuum chamber on anopposite side of said substrate, said photodetector capable of detectingsaid beam of light from said light source through a window in a secondwall of said vacuum chamber when said beam of light encounters anon-circular portion of said substrate as said substrate rotates.
 11. Aprocess capable of degassing a semiconductor wafer in a vacuum chamberand also simultaneously rotationally orienting said wafer in said vacuumchamber which comprises: a) providing a vacuum chamber; b) supporting asemiconductor wafer on an electrostatic clamping structure within saidvacuum chamber to retain said semiconductor wafer in thermalcommunication therewith in said vacuum chamber, said electrostaticclamping structure comprising insulation on a surface thereof facing anundersurface of said wafer, and a high voltage electrode in saidinsulation; c) heating said electrostatically clamped wafer in saidvacuum chamber to a temperature in excess of 350° C. and up to as highas 500° C. to degas said wafer via a heater in said electrostaticclamping structure; d) rotating said wafer in said vacuum chamber up to180° in either one or both directions, using a rotation mechanism toimpart rotation to said wafer in said vacuum chamber, while said waferis being heated sufficiently to degas it and; e) aligning said wafer insaid vacuum chamber using a wafer alignment mechanism capable ofdetermining the rotational alignment of said wafer in response to saidrotation of said wafer in said vacuum chamber, said aligning furthercomprising: i) directing a beam of light perpendicular to the plane ofsaid wafer from a light source on one side of said wafer and adjacentthe periphery of said wafer; and ii) detecting said beam of light fromsaid light source with a photodetector on an opposite side of said waferwhen said beam of light encounters a non-circular peripheral portion ofsaid wafer as said wafer rotates; whereby said semiconductor wafer canbe rotationally aligned while being simultaneously heated to degasifysaid wafer.